In an electronic data storage and retrieval system, a magnetic recording head typically includes a reader portion having a sensor for retrieving magnetically encoded information stored on a magnetic disc. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer or layers of the sensor, which in turn causes a change in the electrical properties of the sensor. The sensing layers are often called free layers, since the magnetization vectors of the sensing layers are free to rotate in response to external magnetic flux. The change in the electrical properties of the sensor may be detected by passing a current through the sensor and measuring a voltage across the sensor. Depending on the geometry of the device, the sense current may be passed in the plane (CIP) of the layers of the device or perpendicular to the plane (CPP) of the layers of the device. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover information encoded on the disc.
Contemporary read heads typically include a thin film multilayer structure containing ferromagnetic material that exhibits some type of magnetoresistance (MR). A typical MR sensor configuration includes a multilayered structure formed of a nonmagnetic layer positioned between a synthetic antiferromagnet (SAF) and a ferromagnetic free layer, or between two ferromagnetic free layers. The resistance of the MR sensor depends on the relative orientations of the magnetization of the magnetic layers.
An MR sensor may include shields consisting of high permeability materials that function to protect the sensor from stray magnetic fields originating from adjacent magnetic bits on the medium. With decreasing sensor size, the shield-to-shield spacing of the MR sensor should be made smaller to adequately screen the flux from adjacent bits. However, the seed and cap layers of the magnetic sensor occupy a large proportion of the total stack thickness and provide a limit to the reduction of the shield-to-shield spacing for magnetic sensors.